Unless they have a new, acceptable contract from the government, unionized air traffic controllers plan to strike at 7 a.m. Monday, an action that could affect up to 75 percent of the nation's 14,000 daily scheduled flights.

Robert E. Poli, president of the nearly 15,000-members Professional Air Traffic Controllers Organization, issued the strike warning yesterday, three days after 95.3 percent of his members voted against a 42-month tentative agreement with the Federal Aviation Administration.

The rejected agreement was worked out June 22, just hours before a nationwide controllers' strike was scheduled to begin at that date.

Transportation Secretary Drew Lewis yesterday caled the rejected pact "fair and equitable," and criticized the PATCO leadership for setting a strike would be illegal, would hurt the airlines, inconvenience the traveling public and severely damage an economy that we are all trying to repair."

During a brief meeting yesterday afternoon, Lewis urged Poli to delay for one week the new nogotiations that have been made necessary by the vote against the June 22 pact. The secretary said the postponement was needed in order to give the government a chance to study the proposals Poli presented yesterday.

Poli refused, and Lewis said the refusal was "unfair and irresponsible." Talks asre scheduled to continue at 10 a.m. today.

Lewis has vowed to stay within the $40 million package the administration put on the table in June. Poli insists that package is too small to include his union's primary demands: a shorter workweek and an improved retirement plan.

If Lewis refuses to change his position, one that has received strong bipartisan support in a cost-conscious Congress, "we'll have a strike Monday morning," Poli told reporters.

The controllers, as well as other federal workers, are forbidden to strike by federal law. But Poli said he will tell his lieutenants to start taking a strike vote at midnight Sunday "if we have not received a settlement proposal which our negotiating team determines should be offered to the membership."

The union's bylaws require an 80 percent vote from its bargaining unit -- all controllers covered by a PATCO agreement, both union members and non-members -- to authorize a strike.

The FAA contends that 17,200 of its employes are in that unit. But Poli said that "since it's our union," he and his aides will determine the makeup of the bargaining unit.

If Poli decides that the bargaining unit includes only his 15,000 members, he has a better chance of getting his 80 percent strike authorization vote, should he call for one. Poli got a 75 percent strike vote June 22, a factor he clamis weakened his position at the bargaining table and led him to accept the temporary pact that his members later rejected.

In any case, Poli contends, and other PATCO leaders agre, he now has the clout to win a strike vote.

Interviews with PATCO Washington officials, several of the union's regional vice presidents, and rank-and-file members show they want a new agreement to include:

A shorter work week, by as much as eight hours from the current 40-hour week. Air traffice controllers argue that because of the stressful nature of their job, they need more time off to rest up between shifts and to prolong their careers.

Earlier retirement. Controllers claim that few of their number last long enough on the job, 25 years, to collect full retirement benefits. They often point to FAA statistics, obtained by the union through the Freedom of Information Act, showing that between 1976 and 1979 about 89 percent of the controllers who retired did so for medical reasons before they were eligible for full retirement benefits.

A better economic package than the 6.6 percent increase in compensation offered by on June 22. Controllers argue that increase only included benefits and would be applicable only to the first year of the rejected contract. Government negotiators disagree, saying that the 6.6 percent represents wages and benefits and would be in addition to a 4.8 percent pay increase due all federal workers.

Lewis said the new proposals Poli presented yesterday would cost the government more than $600 million. He said Poli, who refused to discuss the matter with reporters, believed the new proposals would cost about $490 million.